linux-kernel - [PATCH V2 0/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

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Message-ID: <20250529031650.63880-1-qinyuntan@linux.alibaba.com>
Date: Thu, 29 May 2025 11:16:49 +0800
From: Qinyun Tan <qinyuntan@...ux.alibaba.com>
To: Tony Luck <tony.luck@...el.com>
Cc: "H . Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	Reinette Chatre <reinette.chatre@...el.com>,
	Qinyun Tan <qinyuntan@...ux.alibaba.com>
Subject: [PATCH V2 0/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

V2:
- Keep sanity checks in the __mon_event_count to ensure execution occurs
  exclusively on CPUs sharing the same L3 cache cluster
- When reading the top level event, obtain a CPU within hdr.cpu_mask.
  Then use the cacheinfo shared_cpu_map of this CPU instead of using
  hdr.cpu_mask directly
- Adjust code formatting and commit log descriptions.

In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
structure previously relies on the cacheinfo interface to store L3 cache
information (e.g., shared_cpu_map) for monitoring. However, this approach
introduces risks when CPUs go offline:

The ci field in rdt_mon_domain is initialized using the first online CPU
of a NUMA node. When this CPU goes offline, its shared_cpu_map is cleared
to contain only the offline CPU itself. Subsequently, attempting to read
counters via smp_call_on_cpu(offline_cpu) would fail, but returning zero
values for "top-level events" without error indication.

To resolve these issues:

1. Replace direct cacheinfo references in struct rdt_mon_domain and struct
rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).

2. The hdr.cpu_mask maintained by resctrl constitutes a subset of
shared_cpu_map. When reading top-level events, we dynamically select a CPU
from hdr.cpu_mask and utilize its corresponding shared_cpu_map for resctrl
to determine valid CPUs for reading RMID counter via the MSR interface.

Qinyun Tan (1):
  x86/resctrl: Remove unappropriate references to cacheinfo in the
    resctrl subsystem.

 arch/x86/kernel/cpu/resctrl/core.c |  6 ++++--
 fs/resctrl/ctrlmondata.c           | 13 +++++++++----
 fs/resctrl/internal.h              |  4 ++--
 fs/resctrl/monitor.c               |  6 ++++--
 fs/resctrl/rdtgroup.c              |  6 +++---
 include/linux/resctrl.h            |  4 ++--
 6 files changed, 24 insertions(+), 15 deletions(-)

-- 
2.43.5